Here is a random story that was selected at random as a sample. It is so random, in fact, that I have not even read it myself.
http://www.foxxytheater.com/booksample/
As for the art, most of the covers clearly go with the matching story, as they are made up to look like book covers. There are photo sets with some of them. At the time I purchased this collection, it was expressed to me that copyright is included with the rights to all stories.
As far as the average length, I can only assume that the one in the sample is an average representation. I opened a lot of them and scrolled through them, but not too much more than that. I had purchased them to use on one of my own sites, but since it seems I'll never get around to that and since resale rights were included, I thought just passing them on would be a better use.